In contrast to previous work on lens homogenates, we propose to measure the diffusion coefficient of heavy molecular weight protein aggregates in intact rabbit lenses. Each rabbit lens will be exposed to a 500 rad dose of x-rays causing radiation cataracts to develop. Diffusion coefficient measurements will be made in vitro as a function of temperature, position in the lens, and time after radiation exposure. These measurements will be made using intensity fluctuation spectroscopy. They will determine the percentage of light scattered by cataracts due to protein aggregation as opposed to changes in the structure of the lens. The data also will be analyzed to produce a model of the kinematics of aggregation during cataract development.